The present invention relates to a rotating electric machine with homopolar double excitation. The goal of the invention is in particular to facilitate the passage of the double excitation flux inside the electric machine.
The invention finds a particularly advantageous, but not exclusive, application in synchronous electric machines intended to be used with electric or hybrid vehicles combining the use of a combustion engine and an electric machine.
Rotating electrical machines with double excitation are disclosed in the French patent application number FR-2846483.
As shown in FIG. 1 herein, such machines 1 have a stator 3 and a rotor 5 separated from each other by a functional air gap 6.
More precisely, stator 3 comprises an annular lamellar magnetic core 7 provided with a stator coil 8 and annular coils 9, 10 generating a double excitation flux. Core 7 and stator coils 9, 10 are arranged in a solid magnetic ring 11 in contact with the exterior surface of core 7. This ring 11 comprises at each extremity a rim 13, 14 facing the rotor 5.
Rotor 5 contains a body 15 comprising permanent magnets 18 with tangentially oriented magnetization (perpendicular to the rotor radius) and separated from each other by teeth 19 (FIG. 2) composed of lamellar plates which channel the flux generated by magnets 18 and direct it to the air gap 6.
Rotor 5 further comprises annular flanges 21, 22 positioned on opposite sides of body 15, each having peripheral portions defining, with the radial extremity rims 13 and 14 of the stator ring 11, air gaps for return of the magnetic flux. The flanges 21 and 22 are connected to teeth 19 in an alternating manner. Each tooth 19 comprises an extremity facing towards flange 21 and an extremity facing towards flange 22.
With such an arrangement the excitation coils 9, 10 can modulate the flux of magnets 18 by creating a flux, called double excitation flux, which circulates through paths 24 and 25 passing through stator ring 11, a radial extremity rim 13, 14, a flange 21, 22, the laminations 19 of the rotor, first in an axial direction along the active length D of the machine, then in a radial direction, then through the magnetic core 7 of the stator, closing the loop with ring 11.
Given that the excitation coils 9, 10 have an annular shape and that rotor 5 is made of lamellar material, the reluctance seen by the double excitation flux is high, which penalizes the yield of the machine 1. In order to minimize this reluctance, it was first contemplated to replace this lamellar rotor 5 by a solid rotor, but the core losses would then be excessive. Therefore, it seemed advantageous to combine in the rotor, according to the invention, a lamellar circuit in the periphery (to minimize the losses) and another solid circuit (to facilitate the passage of flux).
However, in the case of a rotor with tangential magnetization, the practical execution of the invention is difficult, in particular because of reasons of mechanical strength, construction complexity, or small improvement in flux circulation.
We also know double excitation electric machines with radial magnets, like those described in U.S. Pat. No. 5,682,073 to Mizuno, using a single excitation coil positioned in the middle of the stator. In this case, it is possible to create a lamellar and solid rotor as in the invention. However, if the rotor according to the Mizuno patent is combined with the stator according to French App. No. 2846483, the obtained electric machine will not function correctly because there would be a magnetic short circuit penalizing the correct circulation of the flux in the machine.